The present invention relates to a photo detection circuit capable of detecting luminance, to a method of controlling the same, to an electro-optical panel, to an electro-optical device, and to an electronic apparatus.
A backlight is provided on a rear surface of a liquid crystal panel of a transmissive or transflective liquid crystal device. The liquid crystal panel modulates light emitted from the backlight. A plurality of pixels are formed in a matrix in the liquid crystal panel, and the transmittance of each pixel is adjusted to display an image. In such a liquid crystal device, the power consumption of the backlight is large. Accordingly, the photo detection circuit is provided in order to reduce the power consumption of the liquid crystal device, and the intensity of the backlight is adjusted according to the intensity of environmental light (for example, see Japanese Unexamined Patent Application Publication Nos. 5-265401 (Claim 1 and FIG. 2) and 6-11713 (Claim 1 and FIG. 1)). In addition, the photo detection circuit is formed on a glass substrate of the liquid crystal device in order to reduce the number of components (for example, see Japanese Unexamined Patent Application Publication No. 2000-131137).
Generally, a current must be extracted from a reverse-biased photodiode in the photo detection circuit as a signal. However, a space for disposing the photodiode within the liquid crystal device is limited, so that the signal current becomes small. Accordingly, it is preferable to extract it as a voltage having a value converted from the current. A method has been proposed in which a potential difference from the signal current is detected by providing a resistor suitable for extracting it as a voltage value.
However, the signal current of the photodiode is very small, so that the resistor must have a high resistance value in order to convert the signal current to a sufficient voltage value. A material having a low resistance value is basically used for a group of wiring lines on the glass substrate of the liquid crystal device, so that it is difficult to form a resistor having a suitable resistance value.